4 DE. J. F. GEMMILL ON THE DEVELOPMENT OF 



11. Ovaries and Ova. 



The gonads are in pairs, interradially placed, and confined to the disc. Each consists 

 of a bunch of short tubes, whitish in the male and orange-coloured in the female. 

 These are attached to the inner aspect of the body-wall close to the mid-interradial 

 line, a short distance upwards from the margin on the aboral side. Here the body- 

 wall is pierced by the egg-ducts. 



In full-grown specimens the number of egg-tubes in each gonad may amount to 

 several hundreds. These are somewhat indistinctly divided into a few (5-7) main 

 groups, which in turn are capable of subdivision into small ultimate clusters of three 

 to seven tubes. The tubes in each of these clusters join together at their attached 

 ends to open into the same terminal branch of the egg-duct. While the majority are 

 cylindrical or sausage-like in shape, simple branching may occur, characterized usually 

 by a single dichotomous division near the free end, and occasionally also by the 

 presence of one or two short lateral branches on the stem. 



The wall of the egg-tubes consists of outer and inner layers separated by irregular 

 spaces. The outer layer, which is considerably the stronger, is made up of connective 

 and muscular tissue, the fibres of the latter being arranged chiefly in a circular 

 direction. It is covered superficially by cubical ciliated cells, and during life the 

 ciliary movement is such that currents of coelomic fluid pass along the surface of the 

 tubes from their attached to their free extremities. The inner layer is thinner and 

 consists almost entirely of connective tissue, but I find that in addition it contains a 

 number of muscular fibres which are longitudinal in direction and occur chiefly 

 towards the attached ends of the tubes. 



The spaces between the outer and inner layers of the gonad-wall are best developed 

 near the attached ends of the tubes. Here they open into an irregular cavity 

 which almost surrounds the commencement of the egg-ducts, and which in its turn is 

 continuous with one of the genital branches of the aboral circular perihaemal sinus. 

 An open communication is thus established between the aboral sinus and the spaces 

 in the gonad-walls. Along this line of communication occur strands of the tissue 

 interpreted by Ludwig and others as blood vascular or heemal. These strands arise 

 from the haemal tissue within the aboral circular sinus and end by spreading out 

 within the spaces between the inner and outer layers of the gonad-walls as fine 

 branches attached to the inner of these two layers. No open communication exists 

 between the interior of the egg-tubes and the genital sinuses or between either and 

 the cavities of the haemal strands. In the adult Solaster endeca I cannot find definite 

 cellular remains of the genital rachis either in the circular or in the genital sinuses ; 

 but in a young Solaster papposa of an inch and a half in diameter the rachis was 

 still represented, in both these cavities, by a thin solid cord of characteristic cells. 



